1. Field of the Invention
The present invention relates to a camera shake correction system and, in particular, to such shake correction system which drives at least a part of optical members forming a photographing optical system of a camera to stabilize an object light incident on an image pickup surface through the photographing optical system.
2. Description of the Related Art
As a conventional camera shake correction system of the above-mentioned type, there has been known a correction system in which a mirror is disposed inclinably within an optical system of a taking lens to thereby refract an object light about 90.degree., and the mirror is inclined to thereby stabilize the object light incident on the image pickup surface of a camera.
Also, as a mechanism for supporting the above-mentioned mirror, there is used a gimbal mechanism or the like which has two rotary shafts respectively disposed on the X and Y axes and independent from each other. That is, the mirror can be supported by such mechanism such that the mirror can be inclined in all directions.
On the other hand, there is also known another type of correction system which does not use the above-mentioned mirror, but uses a gimbal mechanism or the like to support inclinably the whole taking lens or part of lenses forming the taking lens, and drives the thus supported lens or lenses to thereby stabilize the object light incident on the image pickup surface.
For example, according to a camera shake correction system shown in FIG. 27, a correction optical system 1 is driven in a yawing direction (X direction) and in a pitching direction (Y direction) respectively by drive parts 2A and 2B to surely stabilize an object light on an image surface 3 by means of the movements of the correction optical system 1 corresponding to the camera shake by a photographer (Japanese Patent Publication No.2-96621).
In particular, according to the above-mentioned camera shake correction system, in a lens barrel 4 there are provided two angular speed sensors 5A and 5B which are respectively used to detect angular speeds in the X and Y directions. The detection outputs of the two sensors 5A and 5B are then time integrated by integration circuits 6A and 6B respectively to thereby find the angles of shake of a camera in the X and Y directions thereof, and signals (the control target values of the correction optical system) indicating these shake angles are then output to points of addition 7A and 7B, respectively.
To the input of the addition points 7A and 7B, there are being applied from correction optical position detection sensors 8A and 8B the signals that indicate the current positions of the correction optical system 1, as feedback values. The addition points 7A and 7B output to drive circuits 9A and 9B signals indicating a deviation between these two input signals, respectively. In order to make the above deviation 0, the drive circuits 9A and 9B amplify input signals from a point of addition 16 up to suitable voltage signals and output the voltage signals to the drive parts 2A and 2B. Responsive to the input signals, the drive parts 2A and 2B respectively drive the correction optical system 1 in the X and Y directions to thereby stabilize a picture image on the image surface 3.
In the camera shake correction systems of the above-mentioned mechanical correction type, as the drive means for driving the optical members such as the above-mentioned mirror, lenses and the like, there is often proposed an electromagnetic drive means such as a voice coil or the like. However, such electromagnetic drive means is limited in the response speed thereof and consumes a great amount of electric power.
On the other hand, there is also known another type of camera shake correction system which uses a piezo-electric element as the drive means to drive the above-mentioned optical member.
And, as a sensor to detect the shake of a camera, there is used an angular speed sensor which utilizes a Coriolis force. In general, however, it is known that the output of the angular speed sensor of this type is proportional to angular speeds and includes a drift component. That is, due to the drift component included in the sensor output of the angular sensor, a camera shake correction operation is carried out even though the camera remains still, which gives rise to generation of a distorted image surface in synchronization with the drift component, resulting in the hard-to-see images.
Thus, in order to remove the above-mentioned drift component, conventionally, in the angular speed sensor there is provided an insensitive area which corresponds to the amount of drift.
However, due to the fact that in the conventional camera shake correction system the mirror is disposed within the optical system of the taking lens, the taking lens must be designed in consideration of the mirror and thus the currently available taking lens cannot be used. Also, the conventional mirror support mechanism utilizing the gimbal mechanism is not only complicated in structure and large in size, but also due to play of the bearing portion of such mechanism and accurate correction cannot be realized. Further, when an insensitive area to remove the influence of the drift component is provided in the angular speed sensor for detection of camera shake by use of the Coriolis force, it is impossible to detect slight angular speeds contained in the insensitive area, so that it is hard to correct slight camera shake.
In addition, when the piezo-electric element is used as the drive means to drive the optical members such as the mirror and the like, as shown in FIG. 27, a feedback control is necessary because the piezo-electric element has a so called hysteresis characteristic in which an applied voltage is not proportional to the shift thereof. This requires an angle sensor to obtain a feedback value and causes the control system to be complicated.
On the other hand, when the piezo-electric element is controlled by an open loop, for example, if a camera is moved successively in one direction as in a camera panning operation, then the optical member, just after such movements, reaches the end terminal of the movable range thereof and is caused to stop there. Thus, in this condition, if any camera shake occurs, then the optical member is limited in its movement to the thus stopped side so that a sufficient correction effect cannot be obtained.
In order to solve the above problem, there can be suggested a method in which a parallel resistance is inserted in the piezo-electric element to gradually escape electric charges. Even in this case, however, the optical member cannot move back to the center cf the movable range thereof because of the hysteresis characteristic of the piezo-electric element. That is, this method cannot solve the above-mentioned problem completely.
Further, the conventional camera shake correction system shown in FIG. 27 has two independent control systems in the X and Y directions. Due to the two control systems, this conventional camera shake correction system costs substantially double a correction system using a single control system.